JPH031529A - Method and device for dry etching - Google Patents

Abstract

PURPOSE:To obtain a dry etching device which can contribute to the improvement of element properties by detecting the luminous spectrum intensity of impurities in a film to be etched, and operating the concentration of impurity in the film to be etched based on this luminous spectrum intensity, and setting the etching conditions corresponding to this impurity concentration. CONSTITUTION:This is equipped with a processing chamber 11, wherein a semiconductor substrate, on which a polycide film is formed, and others are put, a detection means 12, which detects the luminous spectrum intensity of phosphorus being added as impurities into a polysilicon film using, for example, a polarizing filter, an operation means 13, which calculates the phosphorus concentration in the polysilicon film based on the luminous spectrum intensity given from this detection means 12, and a control means, which sets the optimum etching conditions corresponding to the output of this operation means 13. Accordingly, if controlling the etching conditions of the polysilicon film based on the luminous spectrum intensity of phosphor, optimization of the etching conditions can be realized with high accuracy.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is suitable for manufacturing semiconductor devices using a so-called polycide film, which has a two-layer structure in which a refractory metal silicide film and a polysilicon film are laminated, for example. The present invention relates to a dry etching method and an apparatus therefor.

[Prior Art] Polysilicon films have traditionally been widely used as gate electrode materials for MO3 type transistors, but recently, as shown in FIG. A so-called high melting point metal polycide film (hereinafter referred to as "polycide film") having a stacked two-layer structure has come to be used. This is because the sheet resistance of polycide film is approximately one order of magnitude lower than that of conventional polysilicon film, which enables faster circuit operation and faster device access. This takes into consideration the stability of the interface with the membrane. In FIG. 7, 1 is a silicon substrate, 2
is the gate oxide film.

Polycide film exhibits properties similar to polysilicon film, and can be etched by dry etching using Freon gas.
Etching processing is possible. When dry etching a polycide film, an etching monitor that utilizes the emission spectrum of fluorine is generally used to detect the end point of etching.

[Problem to be solved by the invention]

However, since the polycide film has a two-layer structure consisting of a lower polysilicon film 3 in contact with the gate oxide film 2, etc. and a high melting point metal silicide film 4 laminated on this polysilicon film 3, this polycide film has a dry When patterning is performed by etching, the sides of the polysilicon film 3 become tapered as shown in FIG. 8(1).
As shown in FIG. 8(2), problems often occur, such as the polysilicon film 3, which is a lower layer film, being undercut with respect to the high melting point metal silicide film 4, which is an upper layer film. becomes. As described above, if the etching process of the polysilicon film 3 in contact with the gate oxide film 2 is not performed satisfactorily, it may not be possible to apply the desired voltage to the gate of an MO3 type transistor or the like, or the desired voltage may not be applied to the gate of the MO3 type transistor. Problems arise such as not being able to achieve operating speed.

The reason why the polycide film cannot be etched well is that the polysilicon film 3, which is the underlying film of the polycide film,
An example of this is the variation in impurity concentration. That is, phosphorus is normally diffused into the polysilicon film 3 in order to reduce its sheet resistance, but the etching rate and side etching amount of the polysilicon film 3 change depending on the concentration of phosphorus. be. The etching rate is the reduction amount of the polysilicon film per unit time, and the side etching amount is the lateral etching rate per unit time, that is, the reduction of the polysilicon film 3 with respect to the high melting point silicide film 4 in FIG. 8(2). This means the amount of undercut.

In FIG. 9, a curve 11 shows the dependence of the etching rate of the polysilicon film on the phosphorus concentration, and a curve 12 shows the dependence of the side etching amount on the phosphorus concentration. From FIG. 9, it is understood that the etching rate changes almost in proportion to the phosphorus concentration in the polysilicon film, and the side etching amount follows an almost quadratic curve as the phosphorus concentration in the polysilicon film increases. It can be seen that it is rapidly increasing.

As described above, the amount of side etching changes greatly depending on the change in the phosphorus concentration in the polycide film, so it is difficult to stably etch the polycide film into the ideal cross-sectional shape shown in Figure 7. It's not easy.

SUMMARY OF THE INVENTION An object of the present invention is to provide a dry etching method and apparatus that can solve the above-mentioned technical problems and contribute to improving the characteristics of semiconductor devices, for example.

[Means to solve the problem]

The dry etching method of the present invention detects the emission spectrum intensity of impurities in the film to be etched, calculates the impurity concentration in the film to be etched based on this emission spectrum intensity, and adjusts the etching conditions in accordance with this impurity concentration. It is characterized by setting.

Further, the dry etching apparatus of the present invention includes a detection means for detecting the emission spectrum intensity of impurities in the film to be etched, a calculation means for calculating the impurity concentration in the film to be etched based on the output of the detection means, and a calculation means for calculating the impurity concentration in the film to be etched based on the output of the detection means. and control means for setting etching conditions in response to the output of the means.

[Effect]

According to the structure of the present invention, the impurity concentration in the film to be etched is calculated from the intensity of the emission spectrum of the impurity in the film to be etched, and the etching conditions corresponding to this impurity concentration are set. Etching can be performed satisfactorily by setting optimum etching conditions for the film to be etched.

[Embodiment] FIG. 1 is a conceptual diagram showing the basic structure of a dry etching apparatus according to an embodiment of the present invention.

In this embodiment, with the configuration shown in FIG. 1, a so-called high melting point metal polycide film (hereinafter referred to as a "polycide film") having a two-layer structure, for example, a high melting point metal silicide film and a polysilicon film which is a film to be etched is laminated. ) dry etching is performed. The dry etching apparatus of this embodiment includes a processing chamber 11 in which the semiconductor substrate on which the polycide film is formed, and a polarizing filter for detecting the intensity of the emission spectrum of phosphorus added as an impurity in the polysilicon film. The detection means 12 used,
A calculating means 13 calculates the phosphorus concentration in the polysilicon film based on the emission spectrum intensity given from the detecting means 12, and an optimum etching condition (in this embodiment, an and a control means 14 for setting the etching time.

FIG. 2 is a characteristic diagram showing the dependence of the fluorine emission spectrum intensity and the phosphorus emission spectrum intensity on the phosphorus concentration in the polysilicon film when the polysilicon film is subjected to dry etching using a fluorocarbon gas. In FIG. 2, the curve ff1F shows the dependence of the fluorine emission spectrum intensity on the phosphorus concentration, and the curve 2P shows the dependence of the phosphorus emission spectrum on the phosphorus concentration.

As shown in the curve IIF, the fluorine emission spectrum intensity decreases as the phosphorus concentration increases, but this is due to #lJ
As the etching rate increases as the concentration increases, as shown by curve 11 in FIG. 9, the consumption of fluorine radicals increases. have no relationship. As shown in the unidirectional line 2P, the phosphorous emission spectrum intensity is directly affected by the phosphorus concentration in the polysilicon film. Therefore, if the etching conditions for the polysilicon film are controlled based on the intensity of the phosphorous emission spectrum, the etching conditions can be optimized with high precision.

3 and 4 are cross-sectional views showing the state of dry etching of a polycide film according to the structure shown in FIG. 1. FIG. In FIGS. 3 and 4, parts corresponding to those shown in FIG. 7 described above are given the same reference numerals. 5 is a photoresist patterned on the polycide film, and using this photoresist 5 as a mask,
Patterning of the polycide film is performed by dry etching.

In FIGS. 3 and 4, the processing of the polycide film is illustrated in chronological order starting from (1).

In the case of FIG. 4, the phosphorous concentration in the polysilicon film 3 is higher than that in the polysilicon film 3 of FIG. (1
) to (5) approximately correspond to the elapsed time from the start of etching. That is, when simultaneously starting etching of a polycide film using a polysilicon film 3 with a relatively low phosphorus concentration and a polycide film using a polysilicon film 3 with a relatively high phosphorus concentration, the phosphorus of the polysilicon film 3 At the time when the phosphorus concentration is low, the state shown in FIG. 3(3) is reached, while the state of the high phosphorus concentration is shown in FIG. 4(3).

Figure 5 is a diagram showing the time change of the emission spectrum intensity of phosphorus during dry etching, and Figure 5 (1) is a diagram showing the time change of the emission spectrum intensity of phosphorus during dry etching.
This corresponds to the case shown in the figure (when the phosphorus concentration is relatively low), and FIG. 5(2) corresponds to the case shown in FIG. 4 (when the phosphorus concentration is relatively high). In addition, Fig. 6 shows the time change of the emission spectrum intensity of fluorine, Fig. 6 (1) corresponds to the case of Fig. 3, and Fig. 6 (2) corresponds to the case of Fig. 4. Compatible.

First, the case of FIG. 3, that is, the case where the phosphorus concentration of the polysilicon film 3 is relatively low, will be described. Dry etching is started at time t1 in FIGS. 5(1) and 6(1), and etching of the high melting point metal silicide film 4 begins. As a result, the intensity of the emission spectrum of phosphorus increases during the period from time t1, and the intensity of the emission spectrum of fluorine decreases due to the consumption of fluorine radicals. Then, the intensity of each emission spectrum is changed from time t1 to the time when the etching removal of the high melting point metal silicide film 4 is completed, as shown in FIG.
2) During the period until time L2, when the state shown in the figure is reached, the value becomes a constant value.

During the period from time t2, etching of the polysilicon film 3 is started, and the intensity of the phosphorous emission spectrum increases due to the phosphorus contained in the etched polysilicon film 3. The emission spectrum intensity of fluorine decreases from time t2 corresponding to the etching rate of the polysilicon film 3 through the state shown in FIG. 3(3).
During the period up to time t3 when the illustrated polysilicon film 3 is etched away (FIG. 3(4)), each emission spectrum intensity takes on a constant value.

During the period from time t3, over-etching is performed, whereby a portion of the tapered side of the polysilicon film 3 is removed, resulting in the state shown in FIG. 3(5).

In the case shown in FIG. 4, that is, when the phosphorus concentration of the polysilicon film 3 is relatively high, the emission spectra of phosphorus and fluorine exhibit similar changes. In other words, Figure 5 (2)
Etching of the high melting point metal silicide film 4 is started from time T1 in FIG. 6(2), and at time T2, as shown in FIG.
2) The state shown in the figure will be reached. From time T2, etching of the polysilicon film 3 is started, and at time T3, the state shown in FIG. 4(3) is reached. Furthermore, by performing over-etching for an appropriate time in the period from time T3, the fourth
Figure (4) The state shown in the figure is reached. If the overetching time is set to the same length as in the case of FIG. 3, the polysilicon film 3 will be undercut as shown in FIG. 4(5). This is because the amount of side etching depends on the phosphorus concentration in the polysilicon film 3, as described above.

The time period 1 to L2 in FIG. 5(1) and FIG. 6(1) is also the time T1 to T in FIG.
This period corresponds to period 2, but since the refractory metal silicide film 4 is etched during this period, there is no difference in the intensity of the emission spectra of phosphorus and fluorine.

The period from time T2 to time T3 corresponds to the period from time t2 to time t3, and the polysilicon film 3 is etched during this period. Therefore, the phosphorus emission spectrum intensity is strongly influenced by the phosphorus concentration in the polysilicon film 3. Furthermore, since the etching rate of the polysilicon film 3 increases as its phosphorus concentration increases, when the phosphorus concentration increases, the consumption of fluorine radicals increases, and as a result, the intensity of the fluorine emission spectrum decreases. Become. At this time, the intensity of the phosphorus emission spectrum becomes extremely high due to the effects of both the high etching rate and the high phosphorus concentration. That is, during the period during which the polysilicon film 3 is etched (t2 to t3 degrees T2 to T3), a large level difference ΔP (see FIG. 5) occurs in the intensity of the phosphorus emission spectrum.
A relatively small level difference ΔF (FIG. 6) occurs in the intensity of the emission spectrum of fluorine. Furthermore, since the etching rate is higher when the phosphorus concentration is high, the period from time T2 to T3 is shorter than the period from time t2 to t3.

As described above, depending on the phosphorus concentration in the polysilicon film 3, the intensity of the phosphorus emission spectrum changes greatly, and the time required for etching the polysilicon film 3 also changes. Therefore, conversely, it is possible to calculate the phosphorus concentration in the polysilicon film 3 from the length of the period in which the polysilicon film 3 is etched and the intensity of the phosphorus emission spectrum during this period.

In this embodiment, based on the output from the detection means 12 that detects the intensity of the emission spectrum of phosphorus, the calculation means 13
The period during which the polysilicon film 3 is etched (
t2-t3. T2 to T3) (or the length of the period from etching start time tl, TI to etching end time t3°T3 of polysilicon film 3) and the output of the detection means 12 during this period, it is determined that the polysilicon film 3
The phosphorus concentration inside is calculated. For example, in the calculation means 13, a reference value regarding the intensity of the emission spectrum of phosphorus is determined, and the phosphorus concentration is calculated by calculating the difference between this reference value and the output of the detection means 12.

The calculation result (phosphorus concentration in the polysilicon film 3) in the calculation means 13 is given to the l1lJ control means I4. This control means 14 sets an overetching time corresponding to the phosphorus concentration in the polysilicon film 3, and controls the etching process. As a result, etching is completed in the processing chamber 11 in the optimal state shown in FIG. 3 (5) or FIG. 4 (4).

As described above, in this embodiment, the polysilicon film 3
During etching, the phosphorus concentration in the polysilicon film 3, which has a large effect on the etching rate and side etching amount, is quantitatively determined by detecting the intensity of the emission spectrum of phosphorus in the processing chamber 11. Set the overetching time according to the phosphorus concentration,
The processing chamber 11 is subjected to so-called feedback control. As a result, the etching process of the polysilicon film 3 can be performed satisfactorily, and problems such as undercutting of the polysilicon film 3 can be prevented in the polycide film. As a result, a semiconductor integrated circuit using a polycide film can perform its circuit operation well.

In the above-mentioned embodiment, a polysilicon film applied to a polycide film was used as an example of the film to be etched.
This invention can be widely applied to dry etching a film whose etching rate, side etching amount, etc. change depending on the impurity concentration.

Further, in the above-mentioned embodiments, an example was explained in which the over-etching time was controlled as the etching condition, but other etching conditions may be controlled based on the emission spectrum of impurities in the film to be etched.

〔Effect of the invention〕

As described above, according to the present invention, the impurity concentration in the film to be etched is calculated from the intensity of the emission spectrum of the impurity in the film to be etched, and the etching conditions corresponding to this impurity concentration are set. Dry etching can be performed satisfactorily by setting optimum etching conditions for the film to be etched.

As a result, for example, in semiconductor integrated circuits, etc., it is possible to form electrically scratched wires, etc., so that the desired circuit operation can be reliably achieved and the characteristics of the device can be significantly improved. become.

[Brief explanation of the drawing]

FIG. 1 is a conceptual diagram showing the basic configuration of a dry etching apparatus according to an embodiment of the present invention, and FIG. 2 shows the emission spectrum intensity of phosphorus and fluorine in the polysilicon film during dry etching of the polysilicon film. Characteristic diagrams showing dependence on phosphorus concentration. Figures 3 and 4 are cross-sectional views showing the dry etching process of a polycide film in chronological order. Figure 5 is a diagram showing the intensity of phosphorus emission spectrum over time during dry etching of a polycide film. Figure 6 is a diagram showing changes in the intensity of the emission spectrum of fluorine.
The figure is a cross-sectional view showing the structure of the polycide film, Figure 8 is a cross-sectional view showing the case where the polycide film was not properly dry etched, and Figure 9 is the etching rate and side etching amount of the polysilicon film. FIG. 3 is a characteristic diagram showing the dependence on the phosphorus concentration inside. 11...Processing chamber, 12...Detecting means, 13...Calculating means, 14...Controlling means Fig. Fig. Time opening - F! prlvI- Ginkai

Claims (2)

[Claims] (1) Detecting the emission spectrum intensity of impurities in the film to be etched, calculating the impurity concentration in the film to be etched based on this emission spectrum intensity, and setting etching conditions corresponding to this impurity concentration. Characteristic dry etching method. (2) a detection means for detecting the emission spectrum intensity of impurities in the film to be etched; a calculation means for calculating the impurity concentration in the film to be etched based on the output of the detection means; A dry etching apparatus comprising a control means for setting etching conditions.